In the field of semiconductor manufacturing, lithography is generally employed to provide a pattern to a substrate layer. Specifically, an imageable resist is applied to the substrate needing patterning, the imageable resist is then patterned through exposure and development, and the pattern is transferred to the underlying substrate by etching with a plasma of various reactive ion species, e.g. CF.sub.4.
Since the etch rate of most imageable resist films is greater than that of the underlying substrate layer, the imageable resist etches laterally at a much faster rate than the underlying substrate layer. This lateral etching of the imageable resist severely distorts the pattern formed in the substrate layer and prevents the formation of a desired, small feature sized pattern (100 nm or less) on the substrate layer.
Numerous attempts to overcome this problem have been developed and are now in use. One solution to this problem is to change the imageable resist's resistance to oxygen plasma by using a silylation technique. In accordance with prior art silylation techniques, the imageable resist is silylated before the film is patterned. Such silylating techniques are disclosed, for example, in M. Bottcher, et al. "Surface Imaging by Silylation for Low Voltage Electron-beam Lithography", J. Vac. Sci. Technol. B12, 3473 (1994); C. Pierrat, et al. "PRIME Process for Deep UV and E-beam Lithography", Microelectronic Engineering, Vol. 11, 507 (1990); and M. Irmscher, et al. "Comparative Evaluation of Chemically Amplified Resists for Electron-beam Top Surface Imaging Use", J. Vac. Sci. Technol. B12, 3925 (1994).
Despite being successful in altering the etch rate of the imageable resist, this prior art method requires that changes be made in the resist chemistry and thus the exposure and development process. Such changes are not desirable since they introduce additional materials not typically employed in lithography.
Alternative solutions to this problem are even more complex involving, for example, resist films made from multiple layers of various polymers. The use of multi-polymer film layers is disclosed, for example, in M. A. McCord, et al., "Electron Beam Lithography", Chapter 2 of Handbook of Microlithography, Micromachining and Microfabrication, Vol. 1: Microlithography, P. Rai-Choudhury, ed., SPIE Optical Engineering Press, Bellingham, Wash. (1997). Alternatively, resist polymers can be modified to include alicyclic compounds. These compounds increase etch resistance, but they also change the exposure and development properties of the film (R. D. Allen, et al., "Deep-UV Resist Technology", Chapter 4, ibid.).
There is thus a need for developing a new and improved lithography method which can change the etch resistance of the imageable resist without altering any of the resist chemistry. There is also a need for developing a method which could shift the photolithography industry away from complex and expensive multilayer techniques, and perhaps streamline microelectronic fabrication research by decoupling etching properties from exposure properties.